hiroyuki: an egg coddler is very much like a chawan mushi bowl, however much smaller as you can usually only fit in 1 or 2 broken eggs.

typically the eggs are broken in whole (not scrambled) and cheese is added. the whole thing is cooked immersed in boiling water, hence the screw on tops to avoid water getting in. I think this is because european countries seldom had a steamer. The metal loop at the top is for safe removal :)